Limestone degradation

Acid deposition and the associated particulate nitrates and sulfates are implicated in the deterioration of certain sensitive ecosystems, decreased visibility, negative human health effects, and increased degradation of certain stone building materials and cultural resources, especially those made of limestone and marble. Fine particulate nitrate and sulfate particles... 

Total Carbohydrates. The results of the phenol-sulfuric acid tests for total carbohydrates are listed in Table 1. The Lower and Middle Ordovician dolomites and limestones of this area did not yield detectable total carbohydrates, either because they are absent or because of metamorphic degradation. Palacas (5) and Palacas, Swain, and Smith (6), on the other hand, found traces of glucose and other sugars in Lower and Middle Ordovician rocks of Franklin County, Pa. southeast of the Mt. Union area. It appears that the early and medial Ordovician seas of the Mt. Union area may neither have been receiving much carbohydrate material from the lands nor was much being contributed by organisms to the bottom sediments. 

Degradation is not only confined to coal but also occurs with other materials such as iron ore, coke, sinter, limestone and pellets. In fact degradation is a problem in almost all bulk materials handling facilities. 

Recent precipitation parameters common to Indiana have been used to establish the experimental criteria ( ). These included such data as acid content, meteorological data and conditions, chemical composition of the precipitation, etc. Only one degradation parameter was focused upon the cause and effect interaction of pure in leaching structural materials common in Indiana, including bronze, marble, and Indiana limestone. Quantitative data on the contribution of can then be selectively isolated from the overall effects of the complex environmental matrix. With this initial step, the effects of further matrix components (whether cations, anions, or compounds), acting both individually and/or syner-gistically, can then be pursued. 

The addition of adipic acid to limestone-based FGD wet scrubbers results in improved limestone utilization and enhanced S02 sorption kinetics. The use of adipic acid was first proposed by Rochelle (1) and has been tested by the EPA in pilot systems at the Industrial Environmental Research Laboratory, Research Triangle Park, North Carolina and at the TVA Shawnee Test Facility at Paducah, Kentucky. Adipic acid in the concentration range of 1,000-2,000 mg/1 has been found effective as a scrubber additive. During scrubber operation, however, adipic acid is lost from the system in the liquid and solid phase purge streams and by chemical degradation (2,3). 

Tests conducted at the Shawnee Test Facility indicated that adipic acid added to their limestone FGD scrubber did not degrade at pH s below 5. Since these unexpected but favorable results were important to the future application of adipic acid as an FGD additive, independent verification was desired. Radian was contracted by the EPA to carry out a systematic study of the effects of scrubber operating conditions on adipic acid degradation. 

Calcium carbonate, rather than limestone was used as the source of alkalinity for baseline testing. Again, this permitted independent study of limestone components (notably trace metals) on adipic acid degradation. 

The resulting adipic acid degradation rate did not differ significantly from that of limestone alone. In bench-scale tests at Shawnee and Springfield, in which boiler flue gas with fly ash was utilized, no significant effect of fly ash was observed. 

Lower adipic acid degradation rates were observed when Springfield limestone, rather than CaCC>3, was used as the alkaline species. This result is due to the presence of soluble manganese in the limestone. 

Buffer additives are attractive for enhancing SO2 removal and/or CaC03 utilization in lime/limestone slurry scrubbing processes for flue gas desulfurization. This work was sponsored by EPA to provide experimental data on commercial synthesis, gas/liquid mass transfer enhancement, and oxidative degradation of useful buffer additives. 

Quantity and Concentration. Depending on the operating parameters, the degree of degradation, and the tightness of the liquor loop, the quantity of adipic acid required is quite small in relation to the alkali feed. At Shawnee, where a filter is normally used as the final sludge dewatering device, the adipic acid consumption rate is usually less than 10 lb/ton of limestone fed to the system, and sometimes as low as 2 lb/ton of limestone. These values correspond to only 0.6 to 3.0 tons of adipic acid per day for a 500 MW plant. 

Degradation of adipic acid was low, as expected with the low pH operation. The actual-to-theoretical adipic acid consumption ratio was only 1.26 for a rate of 8.7 lb/ton of limestone feed. 

Case 3 — A limestone case with adipic acid addition operated at high pH. Although only 800 ppm adipic acid is required to obtain 90 percent SO2 removal, degradation of adipic acid at high pH requires about five times the theoretical adipic acid addition rate. 

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